1975 15 HP Johnson low spark

jlm1943

Recruit
Joined
Aug 14, 2004
Messages
2
The motor starts easy but is running rough. The no. 1 cyl has a dim spark, replaced top coil but spark is still the same. No. 2 cyl has bright spark. Any suggestions what to check/replace next.
 

RPJS

Lieutenant Commander
Joined
Jul 29, 2002
Messages
1,572
Re: 1975 15 HP Johnson low spark

Hi<br />Before randomly changing parts I would try swapping the parts from #2 cylinder to #1, start with the plug then points ,condencer etc. This will help identify what parts need changing. Having said that ignition parts are not that expensive and you may feel like replacing everything.
 

songdog

Seaman
Joined
Aug 8, 2002
Messages
50
Re: 1975 15 HP Johnson low spark

John<br /> THE pick-up coils were known to be weak in 1974-1975. I've had the same issue in a '74 9.9.<br /><br /> SDS
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: 1975 15 HP Johnson low spark

The best fix for the low tension magneto Johnrudes ('74-'76) was to do away with the ignition system entirely and install the CD ignition from a '77 or newer 9.9/15. You'd need the flywheel, stator plate, mounting base, power pack, coils and L77JC4 plugs. If you're working from a junked later motor, also swap out the exhaust cover and cylinder head. If you're not working from a junked motor, you'll have to fashion a bracket fo mount the power pack. The later exhaust cover plate gives you mounting bosses for the power pack, and the cylinder head gives you a different plug angle that clears the power pack.<br /><br />Lacking an ignition to convert it to, you could try opening up the points a bit. I've been told that to make those ignitions work a little better the mechs would open up the points to about .060". I don't know if it works or not, so take that with a grain of salt...<br /><br />- Scott
 

bencat

Cadet
Joined
Dec 30, 2001
Messages
17
Re: 1975 15 HP Johnson low spark

I have that same engine and am very interested in changing over to the CD wireing system. Does anyone know if the NAPA CD part # 18-5748 all I need besides what is all ready on the engine. Is it a eazy change over. Does whatever pulses the CD unit attach to existing holes on the stator plate or is mounting a problem, Thanks, Ben
 
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